How badly could a reasonably intelligent follower of the selfish creed, "Maximize my QALYs", be manhandled into some unpleasant parallel to a Pascal's Mugging?

They'd be just as subject to it as anyone else. It's just that instead of killing 3^^^3 people, they threaten to torture you for 3^^^3 years. Or offer 3^^^3 years of life or something. It comes from having an unbounded utility function. Not from any particular utility function.